Chemical engineering of surface coatings for natural stones

Natural stones are materials widely used in today’s architecture. White stones (such as marble) and speckled stones (such as granite) are regarded as suitable for decorative purposes and as construction materials. A major challenge with natural stones is that they degrade in nature through weathering effects, such as UV exposure, acid degradation as well as mechanical weathering through salt crystallization and ice formation inside the pores of the stones. The overall objective of this work has been to develop different hydrophobization methods suitable for natural stones, with the goal of minimizing water contact with the stone substrates and consequently deterring weathering effects. Another goal was to develop testing methods for the evaluation of the protective effects of hydrophobic coatings on natural stones, when weathering was concerned. In this study, a hydrophobic pore-lining coating for marble stones was produced via static and dynamic application methods. In the static systems using a total immersion method, a successful hydrophobization of marble stone products with a fluorosurfactant was verified by water contact angle and capillary absorption measurements before and after intentional UV degradation of the outmost modified layer. Optimization of treatment time and solution concentration led to marble stones that were fully protected from water absorption, even if the outermost surface was degraded by UV weathering. The functionalization method for hydrophobization of porous marble networks was further optimized by controlling the vesicle behavior of fluorosurfactants via tuning the solvent polarity and reaction temperature, leading to successful functionalization deep inside the porous network of the marble stones. This was confirmed by removing the outermost surface of the coated stones through mechanical grinding and measuring capillary absorption on the new surface, showing an increase in effective functionalization depth from μm to mm scale. The functionalization process was furthermore refined through the use of a spray coating method. The optimized spray coating conditions yielded an effective penetration of the fluorosurfactant into the pores of marble, ensuring a long-term protection against water uptake through pore wall functionalization. The final coating also displayed anti-graffiti properties, allowing for graffiti paint to repeatedly be easily washed away with a pressure washer 3-4 times. A new coating could be applied when the first coating lost its effectiveness. Lastly, a durable surface coating based on polydimethylsiloxane for granite was studied to inhibit aging effects related to weathering of granite. The impact of several common weathering effects was evaluated by determining the mass loss, water contact angle, capillary water absorption and possible color alterations before and after the surface treatments. An important discovery was that the impact of the weathering tests on the pure granite was in most cases quite small, however, still noticeable and in some cases even considerable (especially concerning salt weathering). Furthermore, it was found out that sufficiently thick PDMS coatings displayed a superior stability in all the studied weathering tests compared to a reference coating, as the impact of weathering on the hydrophobic functionality of the PDMS-coated samples was minimal. Furthermore, due to the excellent water and salt blocking behavior, the PDMS-coated stones displayed an overall better stability against weathering compared to the untreated stones

High-pressure Treatment of DMAc/LiCl Swollen Softwood Pulp

Swollen softwood cellulose pulp in a DMAc/LiCl solvent system was compressed under elevated pressure (up to 900 MPa) in a Bridgman anvil press. The influence of high pressure on two cellulose systems was studied by measuring X-ray diffraction, mechanical and optical properties and observing scanning electron micrographs of the morphology. Compressed swollen cellulose, washed with distilled water, had lower elastic modulus and hardness compared to swollen cellulose washed with a combination of 2-propanol and deionized water. This work showed that material with lower mechanical properties will be affected more by compression and will result in higher mechanical properties after pressure treatment. Transmitted light in the visible range for both systems was increased after elevated pressure was applied. The XRD measurements revealed the decrease of the cellulose crystallinity after high pressure treatment for all swollen cellulose samples. The morphology of the compacted samples showed noticeable differences between the compact smooth surface and the layered core.</p

High-pressure Treatment of DMAc/LiCl Swollen Softwood Pulp

Swollen softwood cellulose pulp in a DMAc/LiCl solvent system was compressed under elevated pressure (up to 900 MPa) in a Bridgman anvil press. The influence of high pressure on two cellulose systems was studied by measuring X-ray diffraction, mechanical and optical properties and observing scanning electron micrographs of the morphology. Compressed swollen cellulose, washed with distilled water, had lower elastic modulus and hardness compared to swollen cellulose washed with a combination of 2-propanol and deionized water. This work showed that material with lower mechanical properties will be affected more by compression and will result in higher mechanical properties after pressure treatment. Transmitted light in the visible range for both systems was increased after elevated pressure was applied. The XRD measurements revealed the decrease of the cellulose crystallinity after high pressure treatment for all swollen cellulose samples. The morphology of the compacted samples showed noticeable differences between the compact smooth surface and the layered core

Hydrophobization of marble pore surfaces using a total immersion treatment method - Influence of co-solvents and temperature on fluorosurfactant vesicle behavior

International audienceA functionalization method for hydrophobization of porous marble networks has been optimized by controlling the vesicle behavior of fluorosurfactants via tuning the solvent polarity and reaction temperature. Total immersion treatments have been used to diffuse and react the investigated fluorosurfactant (Capstone FS-63) deep inside the porous network, which was confirmed through combined mechanical grinding and capillary absorption measurements, showing an increase in effective functionalization depth from mu m to mm scale. This was accomplished by exchanging water with less polar co-solvents such as ethylene glycol or ethanol in the fluorosurfactant solution combined with elevated reaction temperatures, driving the vesicle-surfactant equilibrium towards free surfactants, which have been investigated by dynamic light scattering measurements. Quantitative particle size distributions and diffusion values for the different mixtures as a function of temperature can be correlated to the increased functionalization efficiency. (C) 2015 Elsevier B.V. All rights reserved

Hydrophobization of marble pore surfaces using a total immersion treatment method - Product selection and optimization of concentration and treatment time

International audienceSix products containing either fluorosurfactants or fluorinated polymers have been evaluated for hydrophobization of marble stones by a total immersion method. Successful hydrophobization was verified by water contact angle and capillary absorption measurements before and after intentional UV degradation of the outmost modified layer. Optimization of treatment time and solution concentration concluded that for the best performing product, Capstone FS-63, a 24h immersion in a 10 vol% aqueous solution was required to obtain marble stones fully protected toward water absorption. The presented surface modifications could significantly increase the product lifespan of a variety of marble products

Novel biorenewable composite of wood polysaccharide and polylactic acid for three dimensional printing

Hemicelluloses, the second most abundant polysaccharide right after cellulose, are in practice still treated as a side-stream in biomass processing industries. In the present study, we report an approach to use a wood-derived and side-stream biopolymer, spruce wood hemicellulose (galactoglucomannan, GGM) to partially replace the synthetic PLA as feedstock material in 3D printing. A solvent blending approach was developed to ensure the even distribution of the formed binary biocomposites. The blends of hemicellulose and PLA with varied ratio up to 25% of hemicellulose were extruded into filaments by hot melt extrusion. 3D scaffold prototypes were successfully printed from the composite filaments by fused deposition modeling 3D printing. Combining with 3D printing technique, the biocompatible and biodegradable feature of spruce wood hemicellulose into the composite scaffolds would potentially boost this new composite material in various biomedical applications such as tissue engineering and drug-eluting scaffolds